Change opacity of feather or blend edge with background


I have situation where the roto edge of the foreground talent is a bit on the brighter side in some areas but darker in others, so I set my roto’d shape feather to ‘Inner’ in order to get rid of the bright edge as I increased my feather value.

My question is: is there a where I could possibly set my roto feather to some value that pulls the roto in enough to pretty much eliminate the bright edge (in my case a value of 10), but then use a another node to actually control the just the opacity of the feathered edge?

My thought in doing this would be to maybe be able to use a smaller feather value (less than 10), and then just be able to lower the opacity value of the edge with the feather, so that I won’t lose to much of the talent edge, but be able to lower the opacity until the brightness no longer seems visibile.

Ultimately if there’s a “better” way or specific node to use in order to just blend the roto edge with my replaced background clip, please let me know. Thanks for any help!!!

It sounds like you may want to do some kind of edge extend. That will extend the FG edges within the matte to remove unwanted BG spill.
Adjusting the feather and roto edges themselves is technically incorrect as your matte now no longer represents the FG accurately, imagine if the BG suddenly changed for example.
Not sure the best approach for an edge extend setup in Silhouette though off the top of my head, one of the devs may be able to help with that.

@persyst I suggest checking out the Matte Repair node in the Key node group. If you have individual shapes in the areas that you want to color correct, you can use the Matte Repair’s Opacity, Black Clip, White Clip, Shrink+Grow, Blur and Wrap controls to manipulate the matte. Blur, Shrink+Grow, and Wrap should do want you want.

Thanks, appreciate the incite!

Ah awesome Marco, definitely going to try out the Matte Repair, thanks!!!

Hi Marco,

Could you please tell me what is the correct way to connect the roto node into a ‘matte repair’ node for just growing/shrinking the roto node and then using the adjusted ‘matte repair’ for creating an alpha cut out into another clip?

I have the roto connecting to the ‘matte repair’ input and ‘obey matte’ and the ‘matte’ output view shows the adjustments I’ve made for “growing” the roto, but I’m not sure how to combine the ‘matte repair’ output to another clip I want to cut out from.

Thanks for your help!!!

This will composite the output of the Matte Repair over a background:

This will composite the alpha from the Matte Repair and another Roto node and based on that new alpha will composite the foreground over the background.

Hi Marco, is there a reason i can’t click & enlarge those screenshots you’ve added?

Probably because they are fairly small images.

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Ah thanks, i’ve been playing with video editing for 16+ yrs but only in the last yr or 2 have i been able to afford a decent PC & software, which i love the BBC stuff btw, but i’ve never had to use the node system/tree, it’s a bit mind blowing just to work out the order of things so i’m trying to take in as much as i can Thanks.

Hi Marco,

Great, thanks for this breakdown! Also just wondering, what OUT should I be using use off of a ROTO node (or any node that has multiple outputs) when my final rendered clip is supposed to have a transparent background at some of the areas outside of the roto shapes? I don’t think I have a good understanding of when to use output vs composite vs composite color as my OUTPUT.

Thanks again!!!

Typically, the first (far left) output of the node is what you want. For Roto, if you render the first output as RGBA then you will have exactly what you want. The Roto > Composite output renders the FG input over the BG input while the Roto > Color Composite output renders the shapes over a color.

Hi Marco, thanks for this. I have a situation where my foreground window has some hotspot reflections on it so I used a couple of feathered circles with a 60%ish opacity so that I would lower the brightness of the hotspots, but not completely cut out the hot spots.

I’m not at my computer at the moment, so I don’t remember which comping node I was using, but I was having a problem where it seemed I could only use the composite color (using a black background) output of the roto window comp’d over my cityscape background to be able to see the darkened roto spots, but if I used the left most output, it seemed to ignore the roto completely. Any thoughts on why this might be? I’ll definitely follow up with more accurate info once I can get to my computer. Thanks.

Silhouette is unpremultiplied by default, so the left output of roto will not be over a black background. If you press Shift+0 (zero), the viewer will be in premultiplied mode and the non-rotoed areas will be black.

I feel like what you’re talking about also ties into another situation I also run into all the time which is I don’t understand why when I have a roto shape and my viewer is set to the left output it shows the whole image as if it was not roto’d at all,so I have to set the view to either composite or color composite to get the cut out shape. Does this have something to do with the premultiply settings too? what does the premultiply setting does on different nodes? I don’t think I really understood what it has been doing. Thanks!!

Hi Marco,

Yea so I see now that shift+0 for toggling the premultiply gives me the alpha/black background when viewing the left output on my roto node, awesome thank you. I was able to move all my outputs to the left output and everything looks good!!!

Now the only thing i noticed is that when I view my DEGRAIN node that comes before the ROTO. I have shift+0 again to unpremultiply in order to view my degrain node or even the original clip inputting into the degrain node. Is the someway to be able to view the premultiplied OUTPUT of the roto and the unpremultplied original clip at the same time without toggling shift+0? Thanks again!

No, there is not. Most users are able to visual what the roto is doing by pressing the A key to overlay the alpha as blue over the image. This way there is no need to view in premultiplied mode.